Advances in Materials Research, Vol. 4, No. 3 (2015) 145-164
145
DOI: http://dx.doi.org/10.12989/amr.2015.4.3.145
Biophysical properties of PPF/HA nanocomposites
reinforced with natural bone powder
Nagwa A. Kamel∗1, Samia H. Mansour2, Salwa L. Abd-El-Messieh1,
Wafaa A. Khalil3 and Kamal N. Abd-El Nour1
1
Microwave Physics and Dielectrics Department, National Research Centre, Dokki, Cairo, Egypt,
2
Polymers and Pigments Department, National Research Centre, Dokki, Cairo, Egypt
3
Biophysics Department, Faculty of Science, Cairo University, Egypt
(Received March 19, 2015, Revised November 16, 2015, Accepted November 16, 2015)
Abstract. Biodegredable and injectable nanocomposites based on polypropylene fumarate (PPF) as
unsaturated polyester were prepared .The investigated polyester was crosslinked with three different
monomers namely N-vinyl pyrrolidone (NVP), methyl methacrylate (MMA) and a mixture of NVP and
MMA (1:1 weight ratio) and was filled with 45 wt% of hydroxyapatite (HA) incorporated with
different concentrations of chemically treated natural bone powder (NBP) (5, 10 and 15 wt%) in order
to be used in treatment of orthopedics bone diseases and fractures. The nanocomposites immersed in
the simulated body fluid (SBF) for 30 days, after the period of immersion in-vitro bioactivity of the
nanocomposites was studied through Fourier transform infrared (FTIR), scanning electron microscope
(SEM), energy dispersive X-ray (EDX) in addition to dielectric measurements. The degradation time of
immersed samples and the change in the pH of the SBF were studied during the period of immersion.
Keywords: biodegradable polyester; nanocomposites; bone powder; dielectric spectroscopy; biophysical
properties
1. Introduction
Tissue engineering is a fast growing area of research that aims to create tissue equivalents of
blood vessels, heart muscle, nerves, cartilage, bone and other organs for replacement of tissue
either damaged through disease or trauma (Langer et al. 1993, Ma 2004, Ma 2005). Various
materials have been used as scaffolds for tissue regeneration. Polymers have great design
flexibility because the composition and structure that can be tailored to the specific needs and
therefore have been extensively studied in various tissue engineering applications including bone
tissue engineering (Ma 2008). The most common biodegradable polymers for bone grafts include
poly (glycolic acid) (PGA), poly(lactic acid) (PLA) poly (lactic glycolic acid) (PLGA),
poly(caprolactone) (PCL), poly (propylene fumarate)(PPF) and poly (ethylene glycol)(PEG).
Polymers usually do not meet all the needs for various tissue engineering applications so most
of the polymer based composite materials are designed to provide improved mechanical properties
*Corresponding author, Professor, E-mail: nagwakamel@gmail.com
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ISSN: 2234-0912 (Print), 2234-179X (Online)
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such as strength, stiffness, toughness and fatigue resistance. Therefore, they are frequently used as
biomaterials for orthopedic applications where mechanical properties are a serious concern.
One of these polymers that investigated as an injectable and biodegradable bone cement is poly
(propylene fumarate) (PPF) (Lee et al. 2008a, Lee et al. 2008b) Studies have demonstrated that
PPF scaffolds can be mechanically reinforced through the incorporation of nanoparticles and
nanotubes to form nanocomposites. The inclusion of surface-modified carboxylate alumoxane
nanoparticles (1 wt %) dispersed within PPF/PF-DA has been shown to result in a greater than
3-fold increase in flexural modulus compared to the PPF/PF-DA material alone (Horch et al. 2004).
Further, increasing degrees of nanoparticle loading into the material did not result in significant
loss of flexural or compressive strength (Horch et al. 2004, Shi et al. 2006, Temenoff et al. 2007).
Polymeric networks of poly (propylene fumarate) (PPF) crosslinked with poly (propylene
fumarate)-diacrylate were investigated by Timmer et al. (2003) as an injectable, biodegradable
bone cement. The effect of crosslinking density, medium pH, and the incorporation of
beta-tricalcium phosphate (beta-TCP) filler on the in-vitro degradation of PPF/PPF-DA was
studied. The results showed that the degradation of PPF/PPF-DA networks can be controlled by
the crosslinking density, accelerated at a lower pH, and prolonged with the incorporation of the
beta-TCP filler.
Jayabalan et al. (2011) studied the effect of hydroxyapatite (HAP) on the performance of
nanocomposites of unsaturated polyester, i.e., hydroxy-terminated high molecular weight
poly(proplyenefumarate) (HT-PPFhm), The tissue compatibility and osteocompatibility of the
nanocomposite containing calcined HAP nanoparticles was evaluated. The tissue compatibility
was studied by intramuscular implantation in a rabbit. They concluded that, the nanocomposite
containing calcined HAP nanoparticles is both biocompatible and osteocompatible.
In our previous work (Kamel et al. 2012) polypropylene fumarate (PPF) crosslinked with NVP,
MMA and NVP/MMA and filled with 40, 45 and 50 wt% HA was studied as biodegradable
polyester nanocomposites to be used as bone substitute material. Results indicated that, the
degradation rate decreases with increasing the HA content, the values of the compressive strength
increased by increasing the filler content. The bioactivity of the nanocomposites was confirmed by
different tools such as; Fourier transform infrared (FTIR), scanning electron microscope (SEM),
energy dispersive X-ray (EDX) and dielectric spectroscopy.
In order to design composite biomaterials or to develop already existing composites for the
repair of bone and cartilage, we need to consider and compare the structure and properties of these
nanocomposites with those of the natural tissue (Gaharwar et al. 2011)
Natural bone matrix is a typical example of organic/inorganic composite material consisting of
collagen and mineral (apatite). This natural composite material has an excellent balance between
strength and toughness, superior to either of its individual components (Ma 2008). Previous works
have highlighted the important role of the organic matrix on the mechanical properties of the
whole bionanocomposites (Fantner et al. 2004). A variety of methods have been used to produce
powders from bone (Johnson et al. 2000).
The aim of the present work is to modify the previous studied PPF/HA nanocomposites by
incorporation of different concentrations of natural bone powder (5, 10 and 15wt %). The
dielectric and mechanical properties of the new nanocomposites before and after immersion in
simulated body fluid (SBF) will be studied. The in-vitro bioactivity will be also studied through
the Fourier transform infrared (FTIR), scanning electron microscope (SEM), energy dispersive
X-ray (EDX). The effect of introducing natural bone powder on the biodegradation rate and the
change in pH during immersion in simulated body fluid (SBF) will be taken into consideration.
Biophysical properties of PPF/HA nanocomposites
reinforced with natural bone powder
147
2. Materials methods
2.1 Materials
Diethyl fumarate, 1, 2-propanediol and tetrabutyl titanate as the transesterification catalyst were
reagent grade from Merck, Darmstadt, Germany. N-vinyl pyrrolidone (NVP; freshly distilled) and
methyl methacrylate (MMA; freshly distilled) were obtained from Merck, Darmstadt, Germany.
Benzoyl peroxide, N, N-dimethyl-4-toluidine and hydroxyapatite were obtained from
Sigma-Aldrich (Germany).
2.1.1 Synthesis of fumarate polyester resin
Polypropylene fumarate (PPF) was prepared by the two-stage melt polycondensation method
(esterification and polycondensation) of (1 mol) diethyl fumarate and (2.2 mol) 1, 2-propanediol in
the presence of catalyst. The detailed of preparation and characterization of PPF were described
elsewhere (Kamel et al. 2010).
2.1.2 Crosslinking of the prepared fumarate polyester
Fumarate polyester resin (PPF) was crosslinked with 30% by weight of (N-vinyl pyrrolidone
(NVP) or methyl methacrylate or a mixture of (NVP/MMA) in the ratio of 1:1 by weight using
benzoyl peroxide as initiator (2% w/w).N,N-dimethyl-4-toluidine (0.2%) was added with rapid
stirring, then the mixture was molded using appropriate molds for different tests. Curing occurred at
room temperature (25oC) for 24 h.
2.1.3 Preparation of natural bone powder
The natural bone powder was prepared from freshly removed diaphyses of the calf long bones.
Bones were dissected from the surrounding connective tissues then alkali treated to leave the purely
osseous structure free from all traces of tissues, fat or any organic matter occupying the intraosseous
spaces. In alkali treatment, the bones were broken into small pieces and boiled for hours in a 30%
sodium carbonate solution followed by thorough washing with hot water. The cycle of alkali
treatment was currently repeated till constant weight was reached .The treated bones were then dried
at 100oC overnight and grounded to fine powder in a hardened steel vial. The bone powder was
sieved to obtain suitable particle size (Moharram et al. 2007).
2.1.4 Fumarate polyester nanocomposites
The nanocomposites were prepared by mixing 45 wt% HA containing different concentrations of
natural bone powder (5, 10 and 15 wt %) with a mixture of fumarate polyester resin and crosslinking
agents namely NVP, MMA, and a mix of NVP/MMA in the ratio of 1:1 by weight. All the samples
were left for 24 h at 25°C for curing.
2.2 Characterization techniques
2.2.1 Transmission electron microscope (TEM)
The particle size of HA and NBP was determined using transmission electron microscope model:
Tecnai G 20, Super twin, double tilt and Magnification range up to 1,000,000 xs and applied
voltage200 kV. Gun type: LaB6Gun Japan.
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2.2.2 Scanning electron microscope (SEM), energy dispersive X- ray (EDX)
Morphology of the composite before and after soaking in SBF was studied through scanning
electron microscope coupled with energy dispersive X-ray microanalysis (SEM/EDX, Philips
XL30) Japan.
2.2.3 Fourier transform infrared (FTIR)
The infrared spectrum was recorded by a JASCO FT/IR 300 E Fourier Transform Infrared
(FTIR) Spectrometer (Tokyo, Japan).
2.2.4 Dielectric measurements
The dielectric measurements were carried out in the frequency range 100 Hz up to100 kHz using
an LCR meter, type AG-411 B (Ando electric, Japan). The capacitance C, loss tangent tan δ, and AC
resistance Rac were measured directly from the bridge from which the permittivity ε′, dielectric loss
ε", and Rdc were determined. A guard ring capacitor type NFM/5T Wiss Tech. Werkstatten (WTW)
GMBH Germany was used as a measuring cell. The cell was calibrated using standard materials and
the experimental error in ε′and ε"were found to be ±3% and ±5%, respectively. The temperature was
controlled to 30oC by putting the cell in a digital oven and the experimental error in the temperature
was ±0. 1°C.
2.2.5 In-vitro tests
To assess in- vitro bioactivity, the nanocomposites were soaked in simulated body fluid (SBF) at
37˚C for 30 days, after which they were rinsed gently with deionized water and dried. The disks
were accurately weighed before and after immersion in SBF. The weight loss (WL) was calculated
according to:
WL% = (W0-Wd)/Wd×100
Where Wo the initial weight of the specimen and Wd the weight of the specimen dried after
different degradation times (7, 14, 21 and 28 days). All the measurements were taken in triplicate
and the average values were calculated.
2.2.6 pH measurements
The pH values were measured during soaking in SBF and readings were taken in an mPA-210
pH meter at 37˚C.
3. Results and discussion
3.1 Transmission electron microscope (TEM)
Fig. 1 gives a TEM micrograph of the hydroxyapatite particles used in this study .The image
show that the sample exhibit needle like morphology. The particle size was found to be in the range
of (26 -120) nm. These results are in good agreement with the HA micrographs previously observed
in literatures (Sanosh et al.2009).
TEM for ground bone powder (Fig. 2) reveals the presence of 2 families of particles, needle-like
crystallites of HA (Fig. 2(a)) with needle length lies between 7 and 31nm and a second family of
Biophysical properties of PPF/HA nanocomposites
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149
Fig. 1 TEM micrographs of HA
Fig. 2 TEM micrographs of NBP, (a) needle-like crystallites of HA and (b) plate-like
crystallites of the NBP
plate-like apatite crystallites (Fig. 2(b)) of about 10-12 nm. TEM studies of animal bones have
revealed that regularly arranged hydroxyapatite crystals occur within the collagen matrix in natural
bones (Ozawa and Suzuki 2002).
3.2 Transmission electron microscope (TEM)
FTIR spectra of hydroxyapatite (HA) and natural bone powder (NBP) which recorded in the
spectral region 4000-400 cm-1 are represented in Fig. 3 and the band assignments are given in
Tables 1 and 2.
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Fig. 3 FTIR of (a) HA and (b) NBP
Table 1 FTIR band assignments for HA
Band No.
1
2
3
4
5
Bands (cm-1)
3555
1031
622
603
561
Assignments
Stretching mode of hydrogen-bonded OH- ions
Stretching mode of PO4-3.
Vibrational mode of hydrogen bonded OH- ions
Bending mode of PO4-3.
Bending mode of PO4-3.
Table 2 FTIR band assignment of NBP
Band No.
1
2
3
4
5
6
7
8
9
10
11
12
Bands (cm-1)
3420
3070
2860-2924
1654
1550
1467
1415
1240
1032
870
603
566
Assignments
N-H Stretching of amide A
Amide B
Asymmetric and Symmetric C-H Stretching
C=O stretching of amide I
N-H bending of amide II
Co3-2 vibrations
Co3-2 vibrations
C-O stretch
PO4-3 vibrations
Co3-2 vibrations
PO4-3 vibrations
Bending mode of PO4-2
Biophysical properties of PPF/HA nanocomposites
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Fig. 4 FTIR spectra of PPF/HA/NBP nanocomposites crosslinked with NVP /MMA and filled with
(a) 5 (b) 10 and (c) 15wt% NBP before and after immersion in SBF for 30 days
Fig. 5 Intensities of 566cm-1 band for PPF/HA/NBP nanocomposites crosslinked ith (a) MMA,
(b) NVP / MMA and (c) NVP and filled with 45wt%HAcontaining (5,10 and15wt%NBP) before
and after immersion in SBF for 30 days
PPF/HA/NBP nanocomposites with different crosslinking agents (MMA, NVP/MMA and
NVP) and different concentrations of NBP (0, 5, 10 and 15 wt %) were immersed in SBF. The
outer layer of the samples was peeled and examined by FTIR spectroscopy before and after
immersion for 30 days. The data represented in Fig. 4 for PPF/HA/NBP crosslinked with
NVP/MMA as an example.
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From the figures it is noticed that, there is a similarity between before and after immersion in
SBF and this was expected result when the bioactive layer formed is similar to the filler in the
nanocomposites. On the other hand, the change of the intensity of bands and width at half height
are connected with the process of hydrolysis of the polymer and the breaking of the bonds in the
chain (Chłopek et al. 2010). The intensity at 566 cm-1characteristic of the vibration of the
phosphate group in the HA was chosen for comparing the intensity before and after immersion in
SBF the results are displayed in Fig. 5 for PPF/HA/NBP nanocomposites.
From this figure, it is clear that the intensity of the band at 566 cm-1 was increased. This is a
good evidence for the formation of layer of bone apatite layer onto the surface of the investigated
samples.
3.3 In-vitro studies during immersion in SBF
3.3.1 Weight loss
Fig. 6 shows the degradation rate of the PPF/HA /NBP crosslinked with MMA, NVP/ MMA and
NVP and filled with 10wt%NBP. From this figure it is clear that the degradation rate follow the
order MMA>NVP/MMA>NVP.
The effect of increasing the NBP concentration on the degradation rate of PPF/HA/NBP
nanocomposites is illustrated in Fig. 7 for nanocomposites crosslinked with NVP as an example.
From this figure it is clear that the weight loss decrease by increasing the concentration of the NBP.
This decrease in the weight loss may attribute to increasing the content of bone morphogenetic
proteins which resulted in high degree of stability in SBF (Haroun and Migonney 2010). It is worth
to mention that the rate of degradation of the nanocomposites reinforced with bone powder was
significantly slower when compared with those of PPF/HA nanocomposites in our previous study
(Kamel et al. 2012).
Fig. 6 Degradation rate of PPF/HA/NBP nanocomposites crosslinked with MMA,NVP/MMA and
NVP and filled with45wt%HA containing 10 wt% NBP versus time (days)
Biophysical properties of PPF/HA nanocomposites
reinforced with natural bone powder
Fig. 7 Degradation rate of PPF/HA/NBP nanocomposites crosslinked with NVP and filled with
45 wt% HA containing 5, 10 and 15wt % NBP versus time (days)
Fig. 8 The changing in the PH values of the SBF during immersion of PPF/HA/NBP
nanocomposites crosslinked with MMA, NVP/MMA and NVP and filled with 45wt% HA
containing (a) 5, (b) 10and (c) 15wt% NBP
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3.3.2 pH measurements
The pH of the SBF solution during immersion of the samples was measured to monitor the
changes that could be a combination of acidic degradation byproducts resulting from the polymer
and any neutralization effects resulting from the fillers.
The changes of the pH values of the SBF during immersion of PPF/HA/NBP nanocomposites
crosslinked with MMA, NVP/MMA and NVP are shown in Fig. 8.
For all samples, the pH of the SBF decreased at the first 3 days of immersion as a result of
dissolution of the nanocomposites which suggest high reactivity of these nanocomposites. After
that slow decrease in the values noticed till constant values were reached .The lowest values were
ranging from 5-6.4. Maruyama and Ito (1996) reported that the exposure of cells to pH 6.0 for
24-48h had no deleterious effects on cell recovery. Therefore, the small pH change produced by
PPF/HA/NBP nanocomposites may not have serious effects on cellular functions in addition, the
continuous circulation in human body is expected to keep the pH value within an acceptable range.
3.4. Evaluation of the bioactivity of the nanocomposites
3.4.1 Scanning electron microscope (SEM) and energy dispersive X-ray (EDX)
The PPF/HA/NBP nanocomposites crosslinked with MMA, NVP/MMA and NVP, and filled
with different concentrations of NBP were immersed in SBF for 30 days. After the period of
immersion the nanocomposites filled with 10wt% NBP crosslinked with NVP/MMA are illustrated
as an example in Fig. 9. The calcium and phosphorous concentrations before and after immersion
are recorded in Table 3.
From the SEM micrograph before immersion in SBF (Fig. 9(a)) there were no cracks which
indicate good compatibility between organic and inorganic phases.
During immersion in SBF roughness in surface of all the samples can be observed. The
Table 3 Calcium and phosphorous concentrations for the PPF/HA/NBP nanocomposites crosslinked with
MMA, NVP and NVP/MMA and filled with 45wt%HA containing 10 wt% NBP before and after immersion
in SBF for 30 days.
Concentrations of elements (at. %)
Before immersion
After immersion
PPF/HA/NBP crosslinked with MMA
Phosphorus
6.31
7.61
Calcium
9.66
11.98
Molar Ca/p ratio
1.53
1.57
PPF/HA/NBP crosslinked with NVP/MMA
Phosphorus
5.51
18.40
Calcium
9.72
31.53
Molar Ca/p ratio
1.76
1.71
PPF/HA/NBP crosslinked with NVP
Phosphorus
3.81
5.94
Calcium
6.06
10.74
Molar Ca/p ratio
1.59
1.8
Element
Biophysical properties of PPF/HA nanocomposites
reinforced with natural bone powder
155
Fig. 9 SEM micrograph and EDX spectrum of PPF/HA/NBP samples crosslinked with NVP/MMA and filled
with 45wt% HA containing 10 wt% NBP (a and c) before, (b and d) after immersion in SBF for 30 day
roughness increases with increasing the immersion time and the surface began to exhibit surface
pores due to the degradation of the polymer. The degradation of the polymer results in more
exposure of the bioactive HA and NBP fillers to the SBF leading to nucleation of the bioactive
calcium phosphate layer by consuming the calcium and phosphorous ions from the solution.
After 30 days of immersion the surfaces was analyzed by scanning electron microscope (Fig.
9(b)) .The bioactivity of the nanocomposites was confirmed by the presence of small and large
spherical particles with bright color denoting deposition of calcium phosphate particles which
coated all the surfaces. The EDX spectra before immersion (Fig. 9(c)) revealed the presence of
carbon (C) and oxygen (O2) of the polymer, calcium (Ca), phosphorous (P), sodium (Na) and
magnesium (Mg) as a result of incorporation of the bone powder (Miculescu et al. 2011) After
immersion for 30 days in SBF (Fig. 9(d)) the EDX analysis revealed the presence of the same
elements with increases in both calcium and phosphorous signals. The phosphocalcic ratio was
1.57, 1.71 and 1.8 for PPF/HA/NBP crosslinked with MMA, NVP/MMA and NVP respectively
which is comparable with the stoichiometries apatite
3.5 Dielectric measurements
The frequency dependence of the permittivity ε′ and dielectric loss ε" over the frequency range
from 100 Hz-100 kHz and at 30°C for poly(propylene fumarate) (PPF) crosslinked with different
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Fig. 10 The permittivity ε′ and dielectric loss ε" versus frequency f of PPF/HA/NBP nanocomposites
crosslinked with MMA, NVP/ MMA and NVP and filled with 45wt% HA containing 5, 10 and 15wt% NBP
crosslinking agents NVP, MMA and NVP/MMA and their nanocomposites with a fixed amount of
HA 45% containing different concentrations of NBP (5, 10 and 15wt %). The obtained data are
illustrated graphically in Fig. 10.
From this figure, it is seen that ε′ for all investigated samples decreases with increasing the
frequency, which shows anomalous dispersion. The rotational motion of the polar molecules of
dielectric is not sufficiently rapid for attain equilibrium with the field (Pathania and Singh 2009).
This behavior is expected in most polymers dielectrics and is due to the dielectric relaxation
phenomena of the polymer materials. Within the measured frequency range, the dielectric
relaxation involves the dipolar (rotational) polarization, which depends on the molecular structure
of the material. At higher frequencies, the rotational motion of the molecules lags behind the
electric field, leading to reduced permittivity with increasing frequency (Zhan et al. 2011). Such
Biophysical properties of PPF/HA nanocomposites
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high values of ε′ may be due to the interface effects within the bulk of the sample and the electrode
effects and or Maxwell Wagner polarization (Ramesh et al. 2002, Sengwa and Sankhla 2007). The
values of both ε′and ε" are found to be comparable with those found before in literature (Kamel et
al. 2010).
It is also clear that the values of ε′ and ε" increase in the order MMA < NVP/MMA < NVP.
This is may be due to the higher polarity of NVP, (4D) (Hu et al. 2000) compared with that of
MMA, (1.79 D) (Abd-El-Messieh 2002).
On the other hand, the absorption curves of ε" versus the frequency f shown in Fig. 10 are
broad indicating that, in addition to the electrical conductivity, more than one relaxation
mechanism is present (Amor et al. 2009). After subtracting the conductivity term, the analysis of
the absorption curves was done in terms of superposition of Fröhlich function distribution
parameter p=3 and a Havriliak-Negami function with distribution parameter α=0.5 and β=0.5
according to the equations given elsewhere (Abd-El-Messieh and Abd-El-Nour 2003). The
obtained data are given in Table 4.
The first relaxation process, which was ascribed to the Maxwell-Wagner effect, was found to be
on the order of 300 Hz and was unaffected by either filler loading or particle size. Its ε" maximum
frequency values were found to increase with increasing filler loading, as shown in Table 4.
The second absorption region in the higher frequency range could be associated with some local
molecular motions rather than the main chain motion as it is expected to be frozen because the
measurements were carried out at 30oC i.e., lower than the glass transition Tg of the crosslinked
polyester (Mc Morrow et al. 2003). This relaxation corresponds to the terminal polar groups,
carboxyl and hydroxyl functions, and to ester functions in the polymer chain (Havriliak and
Havriliak 1997).
Table 4 Relaxation parameters for PPF/HA/NBP nanocomposites crosslinked with MMA, NVP/MMA and
NVP filled with 45wt%HA containing 5, 10 and 15wt%NBP
NBP content wt%
0
5
10
15
0
5
10
15
0
5
10
15
x10-5(s)
S2
x10-11(S/m)
PPF/HA/NBP crosslinked with MMA
3.79
0.409
4.48
0.522
5.31
0.640
5.71
0.795
PPF/HA/NBP crosslinked with NVP/MMA
2.1
0.722
3.5
0.84
3.9
1.05
4.4
1.42
PPF/HA/NBP crosslinked with NVP
1.80
3.10
5.01
5.30
0.986
1.33
1.83
2.85
1.1
1.3
1.5
1.8
3.9
4.64
6.3
7.66
7.4
8.7
11.4
18.2
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Fig. 11 Example of the analysis for PPF/HA/NBP
nanocomposites crosslinked wit NVP/MMA and
NVP and filled with 45wt% HA containing10 wt%
NBP .The data are fitted by Fröhlich and
Havrilliak Negami Functions in addition to the
conductivity term respectively
Fig. 12 The permittivity ε′ and dielectric loss ε"
versus frequency f of PPF/HA/NBP nanocomposite
crosslinked with MMA, NVP/ MMA and NVP and
filled with 45wt%HA containing (5, 10 and 15wt%
NBP) after immersion in SBF for 30 days
The relaxation time associated with this region is found to be highly affected by the type of
crosslinking agent and follows the order MMA > NVP/MMA >NVP i.e. depending on the molar
volume of the rotating unites and consequently the on relaxation time (Kamel et al. 2010). Example
of the analyses for all nanocomposites filled with 45 wt% HA and 10wt%NBP is given in Fig. 11.
After immersing the crosslinked samples in SBF solution for 30 days, the permittivity ε′ and
dielectric loss ε" were re-measured and given in Fig. 12. Comparing the data obtained before and
after immersing in SBF (Figs. 10 and 12) it is seen that both ε′ and ε" decrease by immersing in the
Biophysical properties of PPF/HA nanocomposites
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159
SBF solution.
This decrease could be due to the formation of apatite structure that takes some ions to crystal
formation where they are no longer mobile and no longer contributing to the dielectric spectrum
(Mohamed et al. 1998). The curves relating ε"and the applied frequency were analyzed into one
process by using Havriliak Negami function in addition to the conductivity term. This is because the
fact that value of τ2 becomes large and consequently that the electrical conductivity becomes
predominant rather than Maxwell Wagner effect. The obtained relaxation data are listed in Table 4.
Example of the analyses is given in Fig. 11 for NVP filled with 45wt% HA containing 10wt% bone
before and after immersing in SBF solution.
Comparing Tables 4 and 5 it is interesting to find that both conductivity and S2 decrease while
a pronouncing increase in 2 is noticed. The increase in 2 reflects an increase in the molar volume
of the rotating unites due to the formation of apatite structure that takes some ions to crystal
formation to become no longer mobile and thus no longer contributing to dielectric spectrum. In
order to find an expression to distinguish between the amounts of apatite structure which is
assumed to be formed by immersing the investigated samples in SBF, the relation ( aft.- bef.)/ bef
was calculated and listed in Table 5. From this table it is interesting to notice that the values of (
aft.- bef..)/ bef increase by the addition bone up tell 10 wt% after which a slight increase was
noticed at concentration 15wt% this increase was found to follow the order NVP>NVP/MMA
>MMA. This finding is found to be comparable with that found before in case of PPF/gypsum
nanocomposites (Kamel et al. 2010).
3.6 Mechanical analysis
The mechanical behavior under compressive forces was studied through the compressive
Table 5 Relaxation parameters for PPF/HA/NBP nanocomposites crosslinked with MMA, NVP/MMA and
NVP and filled with 45wt%HA containing 5, 10 and15 wt% NBP after immersion in SBF for 30 days
NBP content wt%
0
5
10
15
0
5
10
15
0
5
10
15
τ2x10-5(s)
S2
σ x 10-11(S/m)
PPF/HA/NBP crosslinked with MMA
11.00
0.198
1.35
14
0.297
6.27
19
0.432
8.75
21
0.561
14.00
PPF/HA/NBP crosslinked with NVP/MMA
8.8
0.637
3.00
16.01
0.287
7.16
20.12
0.375
9.05
23.02
0.469
10.70
PPF/HA/NBP crosslinked with NVP
8.73
0.394
6.48
15.50
0.709
8.52
26.25
2.83
13.5
28.00
3.62
11.8
(τaft - τ bef) / τbef
1.9
2.13
2.58
2.68
3.19
3.57
4.13
4.05
3.85
4.17
4.25
4.28
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Nagwa A. Kamel et al.
Fig. 13 Example of the analysis for PPF/HA/NBP
nanocomposites crosslinked with NVP and filled with
45wt%HA containing 10wt%NBP(a) before and (b)
after immersion in SBF for 30 days .The data are fitted
by using Fröhlich and HavriliakNegami Functions
respectively
Fig. 14 Compressive stress–strain diagram of
PPF/HA/NBP nanocomposites crosslinked with
MMA, NVP/MMA and NVP and filled with
45wt%HA containing 5, 10 and 15 wt % NBP
before immersion in SBF for 30 days
strength at fracture. It is defined as the maximum stress carried by the specimen during the test
“the peak of the stress-strain curve” (He et al. 2001).
The compressive stress-strain diagrams for the fumarate resin crosslinked with MMA,
NVP/MMA and NVP and filled with 45wt% HA containing different concentrations of NBP (5, 10
and 15wt %) are given in Fig. 14. From the figure it is clear that the incorporation of bone powder
to the PPF /HA nanocomposites resulted in significant increase in the values of compressive
strength .The compressive stress was 139.89, 127.66 and 65.82 Mpa at strain 0.36% for composite
filled with 45wt%HA containing 10wt% NBP and crosslinked with NVP, NVP/MMA and MMA
respectively.
Biophysical properties of PPF/HA nanocomposites
reinforced with natural bone powder
161
Fig. 15 Compressive stress–strain diagram of PPF/HA/NBP nanocomposites crosslinked with
MMA, NVP/MMA and NVP and filled with 45wt%HA containing5, 10 and 15 wt % NBP after
immersion in SBF for 30 days
After immersion the nanocomposites in SBF for 30 days (Fig. 15) the values of the
compressive strength increase to reach 190.37, 175.70 and 140.81 MPa at strain 0.36% for
nanocomposites filled with 10wt% NBP and crosslinked with NVP, NVP/MMA and MMA
respectively. The mechanical properties of poly (propylene fumarate) (PPF)-based composite
material increased with degradation time, which was explained by a crosslinking effect promoted
by complexation between carboxylic groups, formed from PPF degradation and accumulated in
the incubation solution, with divalent calcium ions released from hydroxyapatite (Yaszemski et al.
1996).The results suggest that PPF/HA/NBP nanocomposites with a wide range of mechanical
properties could be applied for different clinical uses.
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Nagwa A. Kamel et al.
4. Conclusions
• Trying to enhance the biological and mechanical properties of the PPF/HA nanocomposites,
different concentrations of chemically treated bone powder (NBP) (5,10 and15wt%) was
incorporated into the PPF/HA 45wt% composite. The FTIR spectra of the NBP samples revealed
the characteristic peaks of a residual organic matrix in addition to the characteristic peaks of the
bone apatite phase (CO3-2 and PO4-3). After immersion in the SBF, the increase in the intensities
of the bands at wave numbers 1030, 566cm-1for phosphate group were more pronounced and
confirmed the bioactivity of such nanocomposites.
• The SEM images and phosphocalcic ratio confirmed that the layer formed on the surface of
the nanocomposites is hydroxyapatite. From the dielectric spectra, after immersion in SBF both
conductivity and S2 decrease while a pronouncing increase in τ2 is noticed. The increase in τ2
reflects an increase in the molar volume of the rotating unites due to the formation of apatite
structure.
• From the mechanical analysis it is found that the incorporation of bone powder to the PPF
/HA nanocomposites resulted in significant increase in the compressive strength .The compressive
strength was 139.89, 127.66 and 65.82 Mpa at strain 0.36% for composite filled with 10wt% NBP
and crosslinked with NVP, NVP/MMA and MMA respectively.
• The degradation rate of these nanocomposites decrease by increasing the bone powder
content. The PH of the SBF solution during immersion the nanocomposites was monitored and
found to be ranging from 5- 6.4.
From the previous results it is concluded that, addition of different concentrations of natural
bone powder to PPF/HA 45wt% nanocomposites leads to: enhancement bioactivity and the
mechanical properties ,decreasing the degradation rate which lead to stability of these
nanocomposites, produce less change in the pH of the SBF solution during the immersion of the
nanocomposites. The results could recommend the NVP/MMA to be used in crosslinking
polypropylene fumarate rather than the expensive monomer NVP and the unrecompensed one
MMA. The PPF/HA/NBP nanocomposites are ideal for bone tissue regeneration. The effectiveness
of the dielectric tool for such studies.
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